The unmanned flying battery pack docked to the top of an electric airplane. Image: Flight of the Century

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The long, high aspect ratio wing is a mainstay of efficient flight. Image: Flight of the Century

Jason Paur
Gear

05.10.12

5:19 pm

Electric Airplane Design Uses Flying Drone Batteries to Boost Range

Image: Flight of the Century

An electric-vehicle veteran is turning his efforts from two wheels to a pair of wings as he sets his sights on electric-powered airplanes for his latest world record attempts.

But Chip Yates isn’t satisfied with simply flying faster and higher than any previous piloted electric airplane, he is completely reinventing how electric airplanes are thought of with an infinite-range aircraft, or at least one that could fly for a very, very long time. The breakthrough idea uses autonomous flying battery packs that can be released when empty, with charged packs flying to the airplane and docking for use as needed.

Like all electric vehicles, the design challenge is all about range, range, range and range. And battery technology is always the excuse for not being able to dramatically increase distance between charges. Historically, one of the biggest challenges for long-range airplanes has been weight. And heavy batteries don’t make for a good mix of range and light designs. So Yates isn’t waiting for any breakthrough in battery technology, and is instead pushing for a breakthrough of his own in how the batteries are used.

When Yates decided he wanted to add to his world records for electric motorcycles, the former Boeing employee opted for a flight across the Atlantic in an electric airplane. For several years Yates and a team of friends developed what would become an electric-powered superbike, which he raced several times and set a world record last year for the fastest electric motorcycle at nearly 200 miles per hour. But it turned out aviation was a more natural fit for Yates. And that’s when work got underway.

“We really were a team of aerospace engineers that did an electric motorcycle first,” Yates said from his shop in California. “So doing airplanes is more so where we belong.”

After deciding on trying to fly a transatlantic route in an electric airplane, Yates immediately ran into the problem of how to fly that far using only electric power. The challenge seems almost insurmountable. Current long-range electric airplanes are able to fly hundreds, not thousands of miles. And many, with less than an hour of flight time, are aimed at the recreational market. The Swiss team building the Solar Impulse aircraft are developing a system what would use the sun to charge batteries and climb during the day, and then fly on battery power while descending during the night. But Yates said he wanted to do it no matter what, and his team immediately started thinking about possible solutions.

“Electric airplanes are already penalized by having batteries with very poor energy density,” Yates says, “and then they’re double penalized by the fact that you can’t get rid of them when they’re dead.”

So he came up with the idea of simply starting with a full load of battery power, and then releasing the battery packs as they were consumed.

The unmanned flying battery pack docked to the top of an electric airplane. Image: Flight of the Century

Like a gasoline-powered airplane, this would mean starting very heavy. The Voyager aircraft weighed just 2,250 pounds before being filled with gas for its record-setting non-stop trip around the world without refueling. Once the tanks were filled, the Voyager weighed 9,695 pounds at takeoff. But with gasoline, as the airplane flies and uses fuel, it loses weight, increasing efficiency and range. Yates imagined by dropping batteries he could accomplish the same thing.

In a brainstorming session the team immediately thought the idea had flaws, one of which is the fallacy of using clean energy but dropping batteries everywhere. So they thought about dropping them with a parachute and recovering them. Better, but still not the best. Then an idea was pitched to put small wings on the battery packs so they could glide to a specific location and would be easier to recover. From that point it wasn’t so much of a leap to then think they could carry fewer batteries, and every time one was released, another winged battery pack could fly up to the plane to resupply the missing power pack.

Since that brainstorming session, they’ve been able to work out the basic details and are convinced the idea of using autonomous flying battery packs is not only feasible, but is something worth pursuing. Yates has just three full-time people working on this project, but there are roughly a dozen who are helping, including engineers from SpaceX and Boeing, “guys who are good at docking,” Yates points out.

Initially the team will use steerable parachutes to try for some of their record-setting flights. Yates says they can immediately increase their range by 40 percent by using a pair of battery packs. Once the first is depleted, it will be jettisoned with the parachute while the remaining pack will be repositioned to maintain the aircraft’s center of gravity. He believes he can increase the range by 90 percent by using and dropping around 10 battery packs.

The long, high-aspect-ratio wing is a mainstay of efficient flight. Image: Flight of the Century

The end goal is to develop the technology that would allow for an efficient mothership of sorts that could fly over very long distances with the autonomous batteries docking and being released during flight from either ground-based airports or possibly even recharging stations at sea (pictured at top).

The project is called Flight of the Century and Yates believes that one of the flying electric aircraft could fly non-stop for weeks, months, years — essentially until the vehicle itself wears out by constantly being recharged with the unmanned flying battery packs.

Yates recently acquired an airplane to begin testing his ideas. He’s starting with an airplane well known for its innovation, long-range capabilities and very famous designer, a Rutan Long-EZ. Designed by legendary aerospace guru Burt Rutan in the 1970s, the Long-EZ — and its predecessor, the VariEze — have set several records, including endurance and distance records. Many of those records were set with Burt’s older brother Dick Rutan at the controls. The older Rutan was also part of the Voyager crew that flew the airplane on its record-setting flight.

The Long-EZ is currently being modified for electric flight, which will include using much of the technology Yates and his team developed for his record-setting motorcycle.

The project is internally funded by Yates’ company W. Morrison Consulting, which has a history of working on government contracts. He says his idea has potential applications in both the civilian and military arenas, but there is not a commitment in either direction at the moment.